The primary objective of the proposed project is to provide preliminary answers to the question: "What are the mechanisms by which early intervention improves outcomes in autism?" The proposed project will use eye- tracking methodology to assess neurocognitive markers of treatment response in young children with autism receiving intensive in-home treatment as part of an ongoing randomized controlled trial. The Early Start Denver Model (ESDM) is a relationship-based behavioral intervention focused on building social motivation using positive emotional feedback with a developmental curriculum. Recent research suggests that the ESDM results in significant intellectual, language, and social improvement in young toddlers with autism. The proposed study will use eye-tracking to measure a number of social information processing variables that are conceptually tied to the core deficits targeted by the ESDM, such as social orienting, social attention, and emotion understanding. Leveraging the randomization procedures and controls of an already funded, ongoing RCT of the ESDM, the proposed study will compare neurocognitive processing differences between the treatment group and a community control group at outcome in order to find neurocognitive correlates of treatment response. A third group of typically developing children will be recruited separately and tested on the same neurocognitive measures in order to provide a benchmark for the degree of normalization in the treatment group. Relationships between eye-tracking measures and broader outcomes (e.g., language, IQ, adaptive behavior), as well as between eye-tracking measures and specific behaviors targeted during the course of treatment will be examined as a way to further test for treatment effects at such relatively subtle neurocognitive levels measured by eye-tracking. This study will provide important knowledge about the potential mechanisms and correlates of treatment change. Understanding mechanisms of change is particularly important because it can lead to further refinements in the way treatment is designed and administered, modifying aspects of treatment that do not relate to underlying mechanisms while enhancing those aspects of treatment that do appear related to change. The data collected will provide and important first step in refining our understanding of a very promising treatment paradigm for young children with autism. Given that early intensive intervention may have the best chance of alleviating some of the most devastating aspects of autism, the opportunity to gain as much knowledge as possible about early treatment makes the knowledge gained from the proposed study particularly timely and important. PUBLIC HEALTH RELEVANCE: The proposed project will use eye-tracking methodology to assess neurocognitive markers of treatment response in young children with autism receiving intensive in-home treatment as part of an ongoing randomized controlled trial. The study will leverage an ongoing NIH funded RCT of the Early Start Denver Model (ESDM) by testing children at outcome on a variety of social information processing variables related to the primary treatment targets of the ESDM. A third independent group of typical children will be recruited and tested to provide a normal comparison point for evaluating clinical significance of group differences in eye- tracking measures.